Fix export service error with the new timetable config schema

[zehata]

Updated the validation logic in the export service

Context

Resolves https://t.me/NUSMods/13264
This was caused by the validation logic in

nusmods/export/src/data.ts

Lines 64 to 71 in f722758

	const timetableSchema = Joi.object().pattern(
	Joi.string(),
	Joi.object().pattern(Joi.string(), Joi.string()),
	);
	const taModulesConfigSchema = Joi.object().pattern(
	Joi.string(),
	Joi.array().items(Joi.array().length(2).ordered(Joi.string(), Joi.string())),
	);

not updated for the updated in timetable config schema.

The systemic problem is that there is currently no test coverage for the export service. It also took a long time to fix because the readme is really outdated.

Other Information

Sample image and pdf output of the export service, showing no regression from before #4225:
My Timetable.pdf

[vercel]

@zehata is attempting to deploy a commit to the modsbot's projects Team on Vercel.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.58%. Comparing base (988c6fd) to head (844fc23).
⚠️ Report is 155 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4277      +/-   ##
==========================================
+ Coverage   54.52%   56.58%   +2.05%     
==========================================
  Files         274      297      +23     
  Lines        6076     6924     +848     
  Branches     1455     1671     +216     
==========================================
+ Hits         3313     3918     +605     
- Misses       2763     3006     +243     

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